As part of the $50 million ad campaign for Paramount Pictures' "Titanic" home video debut Sept. 1, Sprint Corp. begins a promotion this week. Two TV spots, by J. Walter Thompson USA, San Francisco, plug Sprint's offer to reimburse customers for the video's cost if they sign up for long-distance service. Paramount also rolls teaser spots this week. Procter & Gamble Co.'s Max Factor makeup brand, the other video sponsor, will tie its fall line to the movie. Copywriter: Paul Cuneo. Art director: Andy Vucinich.